Quantitative In Vivo Cherenkov Luminescence Imaging and Dosimetry of Yttrium-86-NM600.

Purpose: The expansion of radiopharmaceutical therapy (RPT) development demands scalable preclinical dosimetry methods. While PET and SPECT remain the gold standards, their low throughput and high cost limit large-cohort studies. Cherenkov luminescence imaging (CLI) offers a high-throughput alternative but suffers from depth-dependent attenuation and photon scatter that compromise quantitative accuracy. This work develops and validates a quantitative CLI methodology incorporating attenuation and scatter corrections for accurate preclinical dosimetry.

Methods: Depth-dependent attenuation was characterized using a tissue-mimicking phantom to derive calibration coefficients. Photon scatter was modeled using GEANT4-generated Cherenkov spread functions (CSFs), applied in a depth-weighted iterative Richardson--Lucy deconvolution/reconvolution framework. The method was evaluated in NU/NU mice (n=4) bearing MC38 tumors after injection of $^{86}$Y-NM600, an isotope suitable for both PET and CLI. Liver and tumor activities were quantified at four timepoints using PET and the proposed CLI method. Monte Carlo dosimetry was performed for both modalities.

Results: CLI--PET activity quantification yielded mean errors of 15.4% (liver) and 10.3% (tumor) over the first three timepoints. Tumor absorbed doses from CLI-derived synthetic PET images (3.4 $\pm$ 0.3 Gy/MBq) were statistically indistinguishable from PET-based estimates (3.2 $\pm$ 0.2 Gy/MBq, $p=0.31$). Discrepancies increased at late timepoints due to low activity and background auto-luminescence.

Conclusions: With appropriate depth-dependent attenuation calibration and Monte Carlo--derived scatter correction, CLI can provide quantitative biodistribution and dosimetry estimates comparable to PET. This approach enables high-throughput, low-cost in vivo dosimetry, expanding the feasibility of large-scale preclinical RPT studies.